I personally conducted an extensive search on the subject matter of this specification in the U.S. Patent Office. I uncovered several patents which deal with the pyrolytic application of metal oxide films on the surface of a heated glass substrate which will be discussed hereinbelow. These patents seemed to indicate that no particular controls were required in order to generate a metal oxide film on the surface of a heated glass substrate which would have desirable physical and chemical properties when used, for example, as an architectural glazing. The patents seemed to indicate further that no matter how one went about such a coating process, one would be successful.
In doing research work on pyrolytic coating with spray powder compositions, I learned that certain key parameters must be met in order to develop on the surface of the glass substrate a metal oxide film which would have chemical and physical durabilities necessary if that coated substrate is to be successfully used, for example, in an architectural glazing.
The patents that I uncovered that appear to be of interest are set forth individually hereinbelow.
U.S. Pat. No. 3,081,200, in column 3, line 13, shows that the patentee has sprayed both solutions and powders in order to form pyrolytic metal oxide coatings. The patent examples, however, are directed to solutions of coating materials and no specific instructions are contained in the patent with respect to how one successfully accomplishes the application of powders to form a pyrolytic metal oxide film on a glass substrate. This would lead one to believe that any sort of method would be successful. I have found that the methodology employed to develop such a film on a glass substrate does have to be controlled, as will be discussed in greater detail hereinbelow.
German Pat. Nos. 2,529,076; 2,529,077 and 2,529,079 deal with the development of metal oxide film on a glass substrate.
In the '076 patent, metal salt particles are charged prior to application to a glass substrate which has been preheated to a temperature in the range of from 500.degree. to 650.degree. C. The patent indicates that heat decomposable, organic based metal salts may be used and that a preheated carrier gas may be used for transporting the particles to the glass substrate. The patent teaches that the particles should be charged and distributed in a 90.degree. downwardly directed attitude towards the glass substrate from a gas distributor which extends transverse to the direction of travel of the glass substrate passing therebelow. This patent teaches an electrostatic charging of the particles in order to develop a coated metal oxide film on the glass substrate along with a relatively low velocity discharge of the particles in a direction perpendicular to the glass substrate. I have found in my work that it is not necessary to charge the particles and one should not discharge the particles at a relatively low velocity in a direction perpendicular to the surface of the glass substrate which is to have the metal oxide film developed thereon.
German Pat. No. 2,529,077 discloses a process for forming a metal oxide film on a glass substrate by pyrolytic techniques. The starting material is a powder metal compound which is carried by an inert carrier gas into a cyclone where the smallest particles of the compound are separated from the coarser particles, subsequently carried along by the carrier gas flow to the surface of the glass substrate to be coated. The coarser particles are collected then partially evaported under an inert atmosphere by heating. Thereafter, the resulting metal compound vapors are mixed with the carrier gas which carries the finer particles to the surface to be coated. Thus, this patent teaches the simultaneous application of both relatively fine heat decomposable, organic based metal salts and vaporized material of the same nature to the glass surface which is to have a metal oxide film developed thereon. The patent does not teach any criticality with respect to the coating process in order to develop a metal oxide film on the glass substrate which will have chemical and physical durability which will allow that coated glass substrate to be subsequently used in an architectural product. There is no teaching in this patent that certain spray conditions must be maintained in order to develop a metallic oxide film on a glass substrate which has excellent chemical and physical durability.
German Pat. No. 2,529,079 discloses a method in which relatively large particles of a heat decomposable material are dropped on a glass substrate in order to develop a film thereon. I have found that if relatively large particles are simply dropped upon the surface of a heated glass substrate, these large particles tend to burn at the point of impact on the surface and thereby form a discontinuous, spotted film of inferior chemical and physical durability. This patent does not teach the specific operating parameters which I have found necessary in the application of dry powder, heat decomposable, organic based salts to the surface of a heated glass substrate in order to generate thereon a metal oxide film which has excellent chemical and physical durability under commercial use conditions.
U.S. Pat. No. 3,852,098 discloses a process in which a glass substrate is coated with a metal containing film by heating the glass and contacting the hot glass with a gaseous mixture. The patent does not deal with the application of powder materials directly to the surface of the glass in order to develop a metal oxide coating thereon. Rather, the process disclosed is one which uses as the coating medium a gaseous mixture containing from 40 to 100% by volume of the vapors of a reactive metal compound. The mixture is heated by the glass to a sufficient temperature, causing the metal vapor compound to react, thereby depositing the coating film. This patent deals with coating of a glass substrate with a vapor coating system in which vaporized materials are directed against the surface to be coated. The patent has no instructional value to a skilled artisan with respect to how one would apply a dry powder spray of heat decomposable, organic based metal salts to a heated glass substrate in order to obtain thereon a metal oxide film of superior chemical and physical durability.
U.S. Pat. No. 4,182,783 is a patent directed a vapor deposition process for achieving a metallic oxide film on a glass substrate. The method discloses fluidizing particulate solid coating reactants by first establishing a fluidized bed of disbursed particulate solid coating reactants and thereafter drawing a volume of fluidized gas and suspended particulate solid coating reactants to a vaporizer. An additional volume of gas is mixed therewith and then all of the particulate solid coating reactants are vaporized in the reactant/gas mixture. This reactant/gas mixture is then directed into contact with a hot substrate to be coated in order to deposit a film thereon. This patent has absolutely no teachings directed to the application of dry spray materials onto the surface of a heated glass substrate in order to develop a chemically and physically durable metallic oxide film thereon.
U.S. Pat. No. 4,188,199 discloses a process for forming a metal compound coating on the face of a continuously longitudinally moving glass ribbon. The glass ribbon face is contacted while at an elevated temperature with a fluid medium containing a substance which undergoes chemical reaction or decomposition to form the metal compound on the face. The process includes the steps of discharging at least part of the fluid medium against the face in stream formation having velocity components both in the direction of movement of the glass ribbon and in a direction at an inclination to the face of the glass ribbon at a particular angular attitude. Specific examples contained in the patent show the projection of vaporized metal compounds and fluid mediums onto the surface of the glass. There is contained in the patent no discussion of how one would apply a dry power composition to the surface of a glass ribbon in order to achieve a metal oxide film thereon which has superior chemical and physical durability.
U.S. Pat. No. 4,230,271 discloses an apparatus for evenly and uniformly depositing particulate material suspended in a gas on at least one surface of a substrate. In particular, the substrate may be a strip of glass and the product placed thereon a metal salt. However, the discharge is in a downward direction towards the ribbon of glass. There is no further specific discussion of how to obtain a chemically and physically durable metal oxide coating film on a glass substate or what conditions are necessary to achieve such a coating film when a dry powder spray is being used.
The principal purpose of the method of this invention is to provide a method of placing a metal oxide film on the surface of heated glass substrate which is being moved in a selected direction from a glass manufacturing process, the metal oxide film having excellent characteristics with respect to both chemical durability and physical durability.
More specifically, an object of this invention is to provide a method of placing a metallic oxide film on the surface of a heated glass substrate which is being moved in a selected direction from a glass manufacturing process by the pyrolytic application of a dry, heat decomposable, metallic salt spray powder, the metal oxide film having excellent characteristics with respect to both chemical durability and physical durability